1. Field of the Invention
The invention concerns a circuit for the actuation of liquid crystal layers in mirrors, windows or similar dimmable panes, consisting of two polarization filter layers arranged on transparent support layers and a liquid crystal layer bonded on both sides by conductive layers.
2. Description of the Prior Art
The older German patent application No. P 33 30 305.3 proposed a window consisting of a frame and at least one composite glass pane, wherein the composite glass pane is formed by two polarization filter panels provided on the surface facing each other with an electrically insulating coating and with an electrically actuated liquid crystal layer being included between them. Actuation in this case is effected when a pulse-width modulation electrical potential is applied to one of the conductive layers, said potential being produced by an oscillator as the frequency generator, with a frequency divider, a dimmer switch, a pulse-width modulator and a voltage limiter. The circuit proposed in the older application is not capable of satisfying practical requirements because after extended operation, degeneration phenomena appear in the liquid crystal layer, whereby the optical efficiency of the liquid crystal layer under the same electrical actuation--as viewed over a period of time--is significantly altered.